Audio advancement - why?

Atmasphere - As far as I know class D amps enhance a little bit even harmonics (being slightly tube-like) and not the odd ones. It depends also on output configuration - from what I've heard full bridge amps (Icepower) sound more like very good tube amp while half bridge (Hypex) sound more like very good class AB. Tube amps have capacitors and transformers in the signal path - serious limitation in my opinion.

Eldartford - Early SS amps that won battle with tubes had THD in order of 0.00001% and tons of TIM thanks to insane use of global negative feedback. The problem was that TIM was discovered in 70s'. In really bad case output transistors are momentarily overdriven and stop responding for a moment after transition since charge at the junction is trapped and takes time to get out of the saturation. We don't hear tiny gaps in sound because our brains fills them but it makes us tired after a while. It cannot happen in class D. As for limitation - high power Mosfets are slower and carrier frequency is often too low, limiting bandwidth (smaller Icepowers have higher bandwidth than the large ones). 60kHz bandwidth might sound enough (200ASC) but phase shift jumps to 20 deg at 20kHz. Are harmonics added properly? Mosfets are getting faster and stronger every year and in near future class D will improve even further.
Today's class AB amps have gain before feedback often around 4000 while class A amps have gain of few hundred. I would rather have more THD and less bandwidth than TIM and blown-up upper odd harmonics - but good THD and bandwidth spects sell amplifier.

The way I understood the OP's question (or maybe the question I want the answer for) is why hasn't anyone built transistors that can sound as good as tubes to the ear? I don't think it's the matter of technology today, as we pretty much understand how transistors and tubes sound different. I don't think it's economics either. Imagine iPod with sound as good as good tube headphone amp. I bet whoever that can make transistors with tube sound will make a lot of money.

Actually there are transistor amps that do that, but you can count them on one hand with fingers left over. None of them employ global negative feedback- it seems that NF is a design element that has been holding advancements in audio back.

So far the Ridley Audio amplifier is the best example I have seen of what can be done with transistors. Last I heard, it made 100 watts and cost about $100,000 for a pair. There is a heater circuit for the output devices that makes the amp run every bit as hot as tubes. It is better than many tube amps I've heard.

I have yet to hear a class D amp come close, but that technology is still evolving and may yet bear fruit.

Jylee, you are correct. That was my original question. I also wonder sometimes that maybe SS is better than tubes currently - but maybe are we held back by our own "habits" of listening, such that anything other than tube seems "less" in our world!!
Semi went to the extent of size and Undertow mentioned the iPOD. When I mentioned advancement, I did not mean SIZE. Look at my evolving system - I am going from an integrated to a separate preamp and amp. I still cannot switch to iPOD or data-servers. Maybe they are as good as the current mediums I am using - but maybe I am biased to my current medium and that is preventing me from switching to digital files.
As for music as an art - I completely understand. In fact that is what I "try" convey to my non-audiophile friends. But remember if you can create art using more advance technologies, that can lead to betterment of art - why not explore it? Cave men used rocks, charcoal and other items to create art. Why did modern man come up with ink, paper and other stuff? Maybe SS audio has not been fully explored.
Atmasphere, I understand that humans did advance to Tubes. But looks like they are stuck there :-)

Milpai, true, we are stuck- for now. Believe it or not I would be the first to jump on the transistor bandwagon if I thought I could do it without sonic sacrifice!